Has anybody seen this before?
The C-Channel started to crack during our last qualification match, but at the time it was a very small and thin hairline crack. We didn’t think much of it. Today our scissor lift clicked. We assumed one of the gears skipped a tooth, but in actuality…
Well, a picture is worth a thousand words.
See you Florida teams at State this weekend 
I’ve broken a couple aluminum c-channel pieces like that this year. We replaced them with steel and realized that, at our last tournament, they were both seriously bent. 4 stage scissor lifts put a lot of force on the bottom bars.
I have never seen this myself, but I guess that’s because my team has never attempted to build a scissor lift … We’re more of a twisting axles kind of group. XD
Greetings from team 7121D! We look forward to seeing you at States this weekend! 
Nothing against your team or your design, but as far as I can tell, it looks to be the result of over tightening. But then again, I haven’t seen your designs or your robot, so who am I to judge?
Anyways, congrats on cracking an aluminum c-channel. That must take lots of determination. 
SkyRise has been very rough on parts this year. Not to mention school budgets. Rumor is: back at IFI, they call this game “Cash Cow”.
Our team has been hoping to negate any gain for them by having each of us get one of their Rack Solutions complementary aluminum business card holders. I wonder if they’re Vex legal, since they* are *an IFI product…
That’s kinda normal with a scissor lift, we have bent four rails into circles because a bolt broke and the scissor lift would just bend all the metal in autonomous.
Might be IFI, but not VEX. As a non-functional decoration, sure, use your robot to drive around and hand out business cards!
Wow can’t say I’ve seen a piece of alluminum completely crack before. I’ve seen it bend but that’s about it.
See you at state!
-team 9920 Sailor Robotics
Another team in Colorado broke a C channel completely into two pieces in the middle of a match. They were able to fix it with steel bracing on either side, but had to tear the entire lift apart and redesign with more steel on the bottom to prevent it from happening again.
Wow! The worst our team has done is crack a piece of plexiglass in half. During Sack Attack, a non-regular driver got the plexiglass stuck under part of the field but didn’t notice and kept lifting up. A few seconds later the whole scoop split in half 
but luckily it was after the season had ended. Our scoop had actually broken about 6-7 times before that, but those were minor cracks or breaks that we had clumsily repaired with bars.
It’s a 5 stage scissor geared 21:1 torque with the occasional mistake of using motors with wrong internal gearings. I always assumed that it was due to the weird way they built the lift (the first stage is open a lot while the following 4 are compact, compared to evenly open stages continually)
But still, I always expected them to twist the axle holding the 36 and 12 tooth gear before the channel itself sheared. I guess it must be because the axles are mechanically linked.
My team had also “cracked” the c-channel on our lift.
Just to add to this we’re also replacing the aluminum channel that cracked with steel. With our luck it will bend.
I’ve seen the holes bend and get misshapen but not a full on break. That break looks like a tension pull apart break.
Can you describe the direction of the force vectors that was applied on that c-channel?
Was it a torque from > 18" away of a bunch of pounds giving it grief? How fast was it on a dynamic load perspective crashing into things?
Was all the weight really running through that one point or was it distributed across a few connection points?
I do have a theory the newer aluminum is far weaker than the aluminum sold 3-4 years ago. Have some empirical evidence but I don’t have a proper set of gear to test with like used in college engineering classes or manufacturing QA departments.
This particular piece of C-Channel is at the first stage of our lift. It did have a lot of strain on it and we discovered that a metal 12-tooth was grinding on it a couple weeks ago so that could be part of it. We did fix it before the qualifications.
All of the weight was pretty much on that piece (and the matching piece on the other side) exclusively. The C-Channel was directly mounted to a high strength 84 tooth gear so it dealt with a lot of strain/torque with our 21:1 gear ratio. It probably is a tension break.
Was this on the 84 tooth gear at the break? Did you have a spacer between the c-channel and the gear to make a tight fit? (It may not have been at issue in this case but helps in the bending of the 84 tooth gears)
Was this the center of the X of the scissor on the bottom level? All the weight would be on the one screw right there.
Remember, any commercially available screw can be used. Have you looked at higher strength screws?
Here’s an M6 size titanium screw. Only $2.95 each!
http://www.acerracing.com/ball_bearings/M6x20_TITANIUM_SCREW_Button_Head-1321-82.html
Lower weight than steel… sounds tempting…
Yes, this was attached to the 84 and the center of the X was at the bottom level.
We always use spacers due to the way our lift is designed.
We have not looked at higher strength screws, but I’ll do so after States.
Actually the screw won’t help you. It was a failure of the c-channel not the screw.
Bracing that c-channel is what you need.
Any chance that lowest level can have a I-Beam configuration on the lowest point? i-beams are way stronger than c-shaped beams.
Maybe replace that one piece with steel, but then the hole will deform.
Strengthening that will most likely find the next weakest point which I bet will be the 84 tooth gear.
We had similar issues with the scissor lift we were using at the beginning of the season, although the member we had cracked was probably already weakened due to the fact I had cut the c-channels in half. Our gear ratio was 1:21, so it could be the large amount of torque that was being enacted on the lift.
Look forward to seeing you at States!